The present invention relates to a pattern formation method for forming a resist pattern on a semiconductor substrate in a manufacturing process of a semiconductor device, and also to a surface treatment agent for use in the formation of the resist pattern.
In accordance with improved density and integration of a semiconductor device, there are increasing demands for finer processing techniques in these days.
As first means for attaining a fine processing in a lithography process, a technique for improving adhesion between a semiconductor substrate and a resist pattern has been proposed as disclosed in Japanese Laid-Open Patent Publication No. 58-188132.
As a first example of the conventional technique, a pattern formation method using a resist including, for example, a phenol type resin will now be described.
First, the surface of a semiconductor substrate of silicon is supplied with a surface treatment agent including a silane compound represented by a general formula R.sup.8 SiX.sub.3-n R.sup.9.sub.n (wherein n indicates 0, 1 or 2; X indicates halogen or --OR.sup.10 (wherein R.sup.10 indicates an alkyl group having 1 through 3 carbon atoms); R.sup.8 indicates CH.sub.2 .dbd.CH--, ZCH.sub.2 -- (wherein Z indicates halogen) or a group including: ##STR1## and R.sup.9 indicates hydrogen or an alkyl group having 1 through 3 carbon atoms). Thus, the surface of the semiconductor substrate is made to be hydrophobic, thereby improving the adhesion of the semiconductor substrate.
Next, the resultant surface of the semiconductor substrate is coated with a resist including, for example, a phenol resin, so as to form a resist film. The resist film is exposed by using a desired mask, and then successively subjected to post-exposure bake (hereinafter referred to as the PEB) and development. In this manner, a resist pattern is formed.
As second means for attaining the fine processing in the lithography process, a technique for forming a resist pattern out of a chemically amplified resist utilizing generation of an acid by using, as exposing light, DUV light emitted by an excimer laser as a light source or light with a short wavelength such as EB and X-rays has recently been developed.
Now, the pattern formation method using the chemically amplified resist will be described as a second example of the conventional technique, referring to FIGS. 8, 9(a) and 9(b).
FIG. 8 shows a process flow of procedures in the pattern formation method described as the second example of the conventional technique, and FIGS. 9(a) and 9(b) illustrate the state of a surface of a semiconductor substrate obtained by this pattern formation method.
First, a surface of a semiconductor substrate 1 of silicon is supplied with hexamethyldisilazane (hereinafter referred to as HMDS) serving as a surface treatment agent, thereby making the surface of the semiconductor substrate 1 hydrophobic. Thus, the adhesion of the semiconductor substrate 1 is improved. This process is carried out by bubbling HMDS in a liquid phase with a nitrogen gas and spraying the resultant HMDS for 30 seconds onto the surface of the semiconductor substrate 1 having been heated up to 60.degree. C. as is shown in FIG. 9(a). As a result, H in OH groups existing on the surface of the semiconductor substrate 1 is substituted with Si(CH.sub.3).sub.3 (i.e., a trimethylsilyl group), thereby making the surface of the semiconductor substrate 1 hydrophobic. Thus, the adhesion of the semiconductor substrate 1 is improved as well as NH.sub.3 (ammonia) is generated.
Next, the surface of the semiconductor substrate 1 is coated with a chemically amplified resist so as to form a resist film. The resist film is exposed by using a desired mask, and is then subjected successively to the PEB and the development. Thus, a resist pattern is formed.
In the resist pattern formed on the semiconductor substrate by the pattern formation method described as the first conventional example, the surface of the semiconductor substrate is treated with the aforementioned surface treatment agent, and hence, the adhesion between the semiconductor substrate and the resist pattern is improved. However, in the case where a further fine process is to be conducted in the lithography process, this adhesion is not sufficient. In other words, pattern peeling can be caused, for example, in the formation of a pattern of 0.30 .mu.m or less by using i-line exposure, the formation of a pattern of 0.25 .mu.m or less by using KrF excimer laser exposure, and the formation of a pattern of 0.20 .mu.m or less by using ArF excimer laser exposure.
FIG. 10 is a schematic sectional view of a resist pattern 2 formed on the semiconductor substrate 1 of silicon by the pattern formation method described as the second example of the conventional technique. Specifically, the surface of the semiconductor substrate 1 of silicon is coated with a positive type chemically amplified resist (manufactured by Japan Synthetic Rubber Co., Ltd.; KRF K2G) in a thickness of 0.7 .mu.m, the resultant resist film is exposed with a KrF excimer laser stepper with NA of 0.5 and subjected to the PEB for 90 seconds at a temperature of 100.degree. C., and the resultant is developed by using a 2.38 wt % aqueous solution of tetramethylammonium hydroxide. The thus obtained line and space pattern of 0.25 .mu.m has the sectional shape as is shown in FIG. 10.
In the second example of the conventional technique, an insoluble skin layer 3 is formed on the surface of the resist pattern 2 as is shown in FIG. 10. The insoluble skin layer 3 is formed on the resist pattern 2 owing to different atmospheres in the pattern formation.
The insoluble skin layer 3 on the surface of the resist pattern 2 can harmfully affect subsequent processes, which can disadvantageously decrease a yield of the semiconductor device.